Marathon +'s are HEAVY. The tread (not the side wall) may last longer then the rim. I use them on the rear of my off/on road touring bike. I tried to justify buying one for my commuter/on road toring bike but after picking it up... I went back to the good old Vittoria Randonneur Pro. They don't last as long and are not uber resistant but I like the ride.

As for the goathead question I'd talk the those folks who live in some nasty areas.